System and method for tracking drive frequency of piezoelectric motor

Abstract

A system and method for actively tracking a drive frequency of a piezoelectric motor is disclosed. A drive voltage can be applied at a drive frequency to an active piezoelectric element in the piezoelectric motor. A voltage response can be induced in a passive piezoelectric element that is mechanically coupled to the active piezoelectric element to movably engage the passive piezoelectric element at a voltage response frequency. A phase difference can be determined between the drive frequency and the voltage response frequency. The drive frequency of the active piezoelectric element can be adjusted until the phase difference is within a predetermined parameter.

1. A method for actively tracking a drive frequency of a piezoelectric motor, comprising:
 applying a drive voltage at the drive frequency to an active piezoelectric element in the piezoelectric motor; 
 inducing a voltage response in a passive piezoelectric element that is separate from and mechanically coupled to the active piezoelectric element by an engaging element to movably engage the passive piezoelectric element through the engaging element at a voltage response frequency; 
 determining a phase difference between the drive frequency and the voltage response frequency; 
 adjusting the drive frequency of the active piezoelectric element until the phase difference is within a predetermined parameter. 
 
   
   
     2. A method as in  claim 1 , further comprising scaling the drive voltage applied to the active piezoelectric element to provide a desired velocity output of the piezoelectric motor. 
   
   
     3. A method as in  claim 2 , wherein applying a drive voltage further comprises applying a pulse width modulated drive voltage. 
   
   
     4. A method as in  claim 3 , wherein scaling the drive voltage further comprises measuring the voltage response and adjusting the pulse width modulated drive voltage by changing a duty cycle of a pulse width modulation to scale the drive voltage to provide a desired velocity output of the piezoelectric motor. 
   
   
     5. A method as in  claim 1 , wherein adjusting the drive frequency further comprises adjusting the drive frequency of the active piezoelectric element until the phase difference is within 70±0.5 degrees. 
   
   
     6. A method as in  claim 1 , wherein applying a drive voltage at the drive frequency further comprises applying a drive voltage at greater than 120 KHz. 
   
   
     7. A method as in  claim 1 , wherein applying a drive voltage at a drive frequency further comprises applying a drive voltage at greater than 200 KHz. 
   
   
     8. A system for actively adjusting a drive frequency of a piezoelectric motor, comprising:
 an active piezoelectric element; 
 a passive piezoelectric element separate from and mechanically coupled to the active piezoelectric element; 
 an engaging element located between and mechanically coupled to the active piezoelectric element and the passive piezoelectric element; 
 a voltage source electrically coupled to at least one of the active and passive piezoelectric elements; 
 a drive voltage from the voltage source applied to the active piezoelectric element to cause the active piezoelectric element to expand and contract at a drive frequency; 
 wherein the passive piezoelectric element is movably engaged by the active piezoelectric element at the drive frequency to produce a voltage response at a voltage response frequency; 
 a piezoelectric motor driver configured to measure a phase difference between the drive frequency and the voltage response frequency and adjust the drive frequency until the phase difference is within a predetermined parameter. 
 
   
   
     9. A system as in  claim 8 , wherein the piezoelectric motor driver further comprises a drive voltage scaling circuit configured to scale the drive voltage applied to the active piezoelectric element to provide a desired velocity output of the piezoelectric motor. 
   
   
     10. A system as in  claim 9 , wherein the piezoelectric motor driver further comprises a digital signal processor configured to provide a pulse width modulated drive signal. 
   
   
     11. A system as in  claim 10 , wherein the drive voltage is regulated by changing a duty cycle of the pulse width modulated drive signal to scale the drive voltage to provide a desired velocity output of the piezoelectric motor. 
   
   
     12. A system as in  claim 8 , wherein the piezoelectric motor driver further comprises a phase detector circuit configured to measure the phase difference between the drive frequency and the voltage response frequency. 
   
   
     13. A system as in  claim 8 , wherein the drive frequency of the drive voltage is adjusted until the phase difference is within 5 degrees to 355 degrees. 
   
   
     14. A system as in  claim 8 , wherein the drive frequency of the drive voltage is adjusted until the phase difference is within 70°±5°. 
   
   
     15. A system as in  claim 8 , wherein the piezoelectric motor driver further comprises an active piezoelectric element zero-cross detector and a passive piezoelectric element zero-cross detector, the zero-cross detectors configured to determine if the phase difference between the active and passive piezoelectric elements is leading or lagging. 
   
   
     16. A system as in  claim 8 , wherein the voltage source is configured to apply the drive voltage to an electrode coupled to the active piezoelectric element. 
   
   
     17. A system as in  claim 8 , wherein the voltage source is configured to apply the drive voltage at a drive frequency between 20 KHz. and 350 KHz. 
   
   
     18. A system as in  claim 8 , wherein the piezoelectric motor driver is configured to be connected to a plurality of piezoelectric motors. 
   
   
     19. A system as in  claim 8 , further comprising a driver dock coupled to the piezoelectric motor driver and configured to modify at least one of memory storage capacity and processor speed. 
   
   
     20. A system as in  claim 8 , further comprising a communication port coupled to the piezoelectric motor driver and configured to receive communication from an external digital controller.